The operation of an internal combustion engine, such as, for example, a diesel, gasoline, or natural gas engine, may cause the generation of undesirable emissions. EP-1 416 128 discloses a possible solution for reducing undesirable emissions.
Known internal combustion engines of the four stroke type, typically may have at least one combustion chamber in which a piston is reciprocally moveable. The piston may be driveably connected to a crankshaft via a connecting rod. One end of the combustion chamber may have at least one intake port and an associated intake valve and at least one exhaust port with an associated exhaust valve. Generally, the intake and exhaust ports are provided in a cylinder head. A four stroke internal combustion engine may have an intake stroke in which the intake valve may open an intake port and the combustion chamber may be brought into fluid connection with an air intake system. During the intake stroke, the piston in the combustion chamber may move away from the cylinder head and thus, fresh combustion air may be sucked into the combustion chamber. Subsequently, the piston reverses its direction and moves towards the cylinder head for making a compression stroke.
During the compression stroke the intake valve and the exhaust valve may be closed. At a certain moment during the compression stroke fuel may be injected into the combustion chamber. Next, the fuel/air-mixture in the combustion chamber combusts and the piston motion is reversed and the power stroke takes place. During this power stroke, the combustion energy produced may be converted into kinetic energy of increased piston movement which is transferred to rotation of the crankshaft. After the power stroke, the piston movement reverses its direction and moves towards the cylinder head for making an exhaust stroke. During the exhaust stroke, normally, the intake valves are closed and the exhaust valves are opened.
Several variations to the above basic principle are known, for example, for reducing the generation of undesirable emissions. These emissions, that may include particulates and nitrous oxide (NOx), may be generated when fuel is combusted in the combustion chambers of the engine. An exhaust stroke of an engine piston forces exhaust gas, that may include these emissions, from the engine. If no emission reduction measures are in place, these undesirable emissions may eventually be exhausted to the environment.
Research is currently being directed towards decreasing the amount of undesirable emissions that may be exhausted to the environment during the operation of an engine. It is expected that improved engine design and improved control over engine operation may lead to a reduction in the generation of undesirable emissions. Many different approaches, such as, for example, exhaust gas recirculation, have been found to reduce the amount of emissions generated during the operation of an engine. Unfortunately, the implementation of these emission reduction approaches typically may result in a decrease in the overall efficiency of the engine.
Additional efforts are being focused on improving engine efficiency to compensate for the efficiency loss due to the emission reduction systems. One such approach to improving the engine efficiency involves adjusting the actuation timing of the engine valves. For example, the actuation timing of the intake and exhaust valves may be modified to implement a variation on the typical diesel or Otto cycle known as the Miller cycle. In a “late intake” type Miller cycle, the intake valves of the engine may be held open during a portion of the compression stroke of the piston. It also is known to open the intake valves for some time during the exhaust stroke. Thus, some exhaust gas will enter the air intake system and during the intake stroke re-enter the combustion chamber. This operation is known as in cylinder charge dilution (ICCD) and results in less oxygen being present in the combustion chamber for combustion. Additionally, remaining hydrocarbons in the exhaust gases may be burned after re-entrance in the combustion chamber, thus reducing undesirable emissions.
Under heavy load circumstances, it may be necessary to increase the amount of oxygen into the combustion chamber. Especially with long stroke engines, that have a rather large combustion chamber volume in relation to the diameter of the combustion chamber, during heavy load circumstances the amount of air which can be taken in may be too small. In order to be able increase the possible amount of oxygen as much as possible, the prior art has disclosed multi port engines. Such engines may have two or three intake valves and two or three exhaust valves in each combustion chamber. Of course, there is a limit to this in that the bore area of the cylindrical combustion chamber is limited and must contain both the intake ports and exhaust ports. Research has been directed to turbocharging the intake air, to the shaping of the ports and to the timing of the opening of the intake valves and exhaust valves. Although this research may have led to increase the amount of intake air that can be taken in during the intake stroke, a still further increase would be desirable.
The current disclosure is directed to one or more improvements in the existing technology.